The present invention relates to porous particles of calcium carbonate and a method for the preparation thereof.
Powders of calcium carbonate are widely used in a wide variety of industrial fields, for example, in the industries of rubbers, plastics, paper and paints as a filler or extender, food industries and horticulture. Among various types of the calcium carbonate products under use, the so-called heavy calcium carbonate powder is produced by finely pulverizing naturally occurring calcium carbonate minerals such as limestone, calcite and the like and consumed in large quantities with a rapidly growing demand by virtue of the low production costs as a general-purpose extender in rubbers, plastics and paints.
apart from the above mentioned general-purpose calcium carbonate powders, the trend of demand for calcium carbonate products in recent years is in the direction for products of upgraded properties, in particular, in respect of the particle configuration which is not irregular as in the conventional heavy calcium carbonate powders by pulverization but spherical, columnar, cubic, spindle-shaped, scaly or flaky, whisker-shaped and so on to satisfy the special requirements in novel and unique applications of the powder. Calcium carbonate powders having a porous structure of particles are also highlighted in respect of the relatively low apparent density of the particles and used as a filler of paper, food additive, e.g., as an auxiliary mineral nutrient, carrier of certain liquid materials and the like.
Porous particles of calcium carbonate can be prepared, for example, by the method disclosed in Japanese Patent Kokai 61-168524. The porous particle obtained by this method, however, is an aggregate of finer particles or a so-called secondary particle having a dimension of several micrometers formed by aggregation of a number of primary particles having a dimension smaller than micrometer. Accordingly, such a particle is inherently not porous but the porosity thereof is formed from intercommunicating open void channels between the neighboring primary particles. This product is currently used in applications in which hiding power of the powder is required but not satisfactory in the applications as a liquid absorbent or as a base material for sustained release of certain vaporizable materials. To be satisfactorily used in these applications, it would be important that the primary particles are each inherently porous with a decreased overall specific pore surface area, increased overall pore volume and decreased average pore diameter. The pores in such porous particles each should have an ink bottle-shaped configuration not intercommunicating with the others.